Cutting hole into a face with a line loop?
This can be done using Knife Project, however for the case you show to work, you will have to use a recent Blender build, since improved knife support was added after 2.69 release.


  To use Knife Project, in Object mode select the object you want to project (use and cut the other) first then Shift select the "object to be cut". Now Tab into Edit mode and press Knife project.


 

Before projecting from a text object and Resulting knife projection.